With rapid development of science and technology, portable electronic devices, such as video cameras, laptop computers, portable DVDs, MP4s and digital cameras are becoming increasingly popular in people's daily life. To meet the requirement of being convenient for carrying, lithium ion batteries are widely used as a desirable power source for portable electronic devices.
Lithium ion batteries can supply energy for mobile electronic devices anytime and anywhere. However, due to the use of high-energy chemical materials and energy concentration, safety performance of lithium ion batteries is not satisfactory. For instance, during charge or discharge process of a lithium ion battery, short-circuit possibly occur because of compression, collision or other unexpected incidents, which will inevitably produce large current and generate a lot of heat. The heat accumulation may cause the lithium ion batteries to burn or explode and, therefore, damage the electronic devices and even injure the users.
To improve the safe performance of a lithium ion battery, a safety device is provided on a top cover of the lithium ion battery. The safety device includes a top cover defining an air exhaust hole, a rupture plate electrically connected to a bottom surface of the top cover and sealing the air exhaust hole, a vent plate having an air hole electrically connected with the rupture plate via soldering or riveting, and an insulating gasket for electrically insulating the rupture plate from the vent plate except the soldering point. When the lithium ion battery is overcharged or short-circuited, the expanded air in the lithium ion battery acts on the rupture plate via the air hole and urges the rupture plate to deform upwardly, so as to disconnect the vent plate from the rupture plate and cut off the circuit path. If the air pressure in the lithium ion battery further increase, the rupture plate will break. The air can vent into the surroundings via the air exhaust hole.
However, in the conventional lithium ion battery, there is only one air exhaust hole defined in the top cover. When the rupture plate disconnects from the vent plate, the rupture plate deforms upwardly toward the top cover under the drive of the air pressure. The central portion of the rupture plate may block the air exhaust hole, which may lead to igniting or exploding of the lithium ion battery.
What is needed, therefore, is to provide a safety device with desirable safety performance for use in a lithium ion battery.